Metabolism of prostaglandin D2 in the monkey

[3H7]Prostaglandin D2 was biosynthesized and infused into an unanesthetized monkey. The urinary metabolites were isolated and subsequently identified by gas chromatography-mass spectrometry. Two pathways of prostaglandin D2 metabolism were identified and resulted in metabolites with prostaglandin D (3-hydroxycyclopentanone) and prostaglandin F (cyclopentane-1,3-diol) ring structures. The major prostaglandin D ring metabolite was identified as 9,20-dihydroxy-11,15-dioxo-2,3-dinorprost-5-en-1-oic acid. Nine other prostaglandin D ring metabolites were identified reflecting various combinations of metabolism by beta and omega oxidation, 15 dehydrogenation, and 13-14 reduction. In greater abundance were those prostaglandin D2 metabolites which had the prostaglandin F ring structure. The major prostaglandin D2 metabolite which had the prostaglandin F ring structure was identified as 9,11,15-trihydroxy-2,3-dinorprosta-5,13-dien-1-oic acid (dinor prostaglandin F2 alpha). Nine other metabolites with the prostaglandin F ring structure were identified, including prostaglandin F2 alpha itself. These, for the most part, were the structural counterparts of the metabolites with the prostaglandin D ring. Since many prostaglandin D2 metabolites were found to be identical with the metabolites of prostaglandin F2 alpha, quantitative determinations of prostaglandin F ring metabolites may not be a specific indicator of prostaglandin F2 alpha biosynthesis. Likewise, data involving the measurement of a biological effect of prostaglandin D2 must be re-examined to account for the possible contribution of prostaglandin F2 alpha, a metabolite of prostaglandin D2, to the biological response.

Tartrazine and the prostaglandin system

The effect of tartrazine on prostaglandin production was evaluated in several in vitro systems in order to elucidate the interrelationship between aspirin-sensitive asthma and tartrazine. Unlike the nonsteroidal anti-inflammatory drugs, tartrazine did not inhibit cyclooxygenase activity in sheep seminal vesicles, guinea pig lung microsomes, and human platelets. Tartrazine had no effect on the activation of acyl hydrolase, which is the rate-limiting step in prostaglandin production. The major metabolite of tartrazine, sulfanilic acid, also had no inhibitory effect on the sheep seminal vesicle cyclooxygenase. In view of these findings, if there is a cross-sensitivity between tartrazine and aspirin in aspirin-sensitive asthmatics, it is unlikely to be on the basis of prostaglandin inhibition.

[Action mechanism and clinical indications for thrombocyte aggregation inhibitors]

The mechanisms of action of three most commonly used antiplatelet agents (aspirin, sulfinpyrazone, dipyridamole) are briefly discussed. Aspirin inhibits the prostaglandin synthetase of platelets irreversibly and thereby blocks the production of prostaglandin endoperoxides and thromboxane A2, which stimulate platelet aggregation. A daily aspirin dose of 200--300 mg is sufficient to achieve this effect. Sulfinpyrazone appears to interfere with the adhesion of platelets to subendothelial structures and atherosclerotic plaques. Dipyridamole increases cyclic AMP in platelets and thus reduces platelet response to aggregating agents. A few of the satisfactorily performed studies on the clinical effectiveness of antiplatelet agents are mentioned. Sulfinpyrazone treatment of patients with myocardial infarction (Killip--classification I and II), starting 25--35 days after the acute myocardial infarction, reduces cardiac mortality and incidence of sudden death for a period of two years. The efficacy of aspirin treatment in coronary artery disease is not yet definitely established. In patients with transient ischemic attacks, particularly males with appropriate carotid lesions, aspirin therapy reduces the frequency of transient ischemic attacks and possibly the incidence of stroke and death. Sulfinpyrazone is ineffective in these patients. Sulfinpyrazone and aspirin are of value in the prevention of thrombosis in straight arterio-venous shunts. Aspirin reduces the frequency of deep venous thrombosis after total hip replacement in males but not in females. In patients with recurrent venous thrombosis, sulfinpyrazone treatment is effective in preventing thrombosis.

Effects of feeding ethyl-dihomo-gamma-linolenate on rabbit renomedullary lipid composition and prostaglandin production in vitro

Feeding the ethyl ester of dihomo-gamma-linolenic acid for 25 days to rabbits resulted in increased PGE1 (20 to 30-fold) and PGE2 (1.5-fold) output by a hormone responsive, in vitro, renal papilla preparation. The relative amount of PGE1 increased from less than 5% of PGE2 in controls to 25-35% of PGE2 in the papillae of 20 : 3 omega 6-supplemented animals. During the study renomedullary tri glycerides in the 20 : 3 omega 6-supplemented animals increased 2.8-fold compared to animals fed an equal amount of a control fatty acid mixture, and in addition to a marked enrichment in 20 : 3 omega 6, also contained increased proportions of 20 : 4 omega 6 and longer chain polyenes. The increase in triglyceride content found in the renal medulla was not seen in the renal cortex or liver. There was no increase in renomedullary phospholipid content during the study, and phopholipids of treated animals contained increased proportions of 20 : 3 omega 6 and 20 : 4 omega 6, but not longer chain polyenes. The results indicate that enriching the prostaglandin precursor pool by feeding 20 : 3 omega 6 can alter the type and amount of prostaglandin released by the renal papilla, at least in vitro. Also, the selective changes in amount and long chain polyene content of renomedullary triglycerides during the study suggest some special functions for this lipid class in prostaglandin precursor metabolism.

Relation between plasma concentration of indomethacin and its effect on prostaglandin synthesis and platelet aggregation in man

The dose and plasma levels of indomethacin correlated with inhibition of prostaglandin synthesis as measured both by urinary excretion of the major metabolite of prostaglandin E2 (PGE-M) and by the release of prostaglandin E2 from thrombin-stimulated platelets. Considerable intersubject variability was observed in the suppression of PGE-M excretion. In some patients 37.5 mg indomethacin daily, usually considered subtherapeutic, caused suppression. Maximal suppression (greater than 90%) occurred in some after a daily dose of 75 mg, whereas 150 mg was required to achieve this level of inhibition in others. Suppression of the excretion of PGE-M by 60% occurred when the end of the dosage interval plasma levels of indomethacin were in the range 0.05 to 0.3 microgram/ml, which implies that a somewhat higher average steady-state concentration during the dosage interval was required to achieve this effect. A similar degree of inhibition of the release of PGE2 on thrombin-stimulated platelets was associated with the same range of plasma levels. Upon discontinuation of the drug, the levels of indomethacin in plasma decreased exponentially; inhibition of the release of PGE2 from platelets by indomethacin declined linearly with time and in parallel with the logarithm of the diminishing plasma levels.

Prostaglandin D2, another renal prostaglandin?

Prostaglandin (PG) D2 was biosynthesized by rabbit renal papillae incubates in vitro. Quantification of the renal prostaglandins by gas chromatography-mass spectroscopy demonstrated that the concentration of PGD2 generated by renal papillae was 1/6 to 1/10 the amount of PGE2 or about 1microgram/g tissue/30 min. Infusion of the sodium salt of PGD2 into the renal artery of the dog produced a dose related increase in renal blood flow and urine flow, free water clearance, sodium excretion and potassium excretion without changes in systemic hemodynamics. At low doses PGD2 increased renal blood flow to all cortical zones. Higher concentrations of PGD2 produced a shift in the intrarenal distribution of blood flow toward the juxtamedullary nephrons.

Synthesis and metabolism of prostaglandins E2, F2alpha and D2 by the rat gastrointestinal tract. Stimulation by a hypertonic environment in vitro

Whole cell preparations of rat stomach corpus, jejunum, and colon were incubated and the released prostaglandin E2 (PGE2), PGF2alpha, PGD2, 15 keto-13,14 dihydro PGE2, and 15 keto-13, 14 dihydro PGF2alpha were measured by combined gas chromatography-mass spectrometry. All regions made PGD2 and possessed a high capacity for production 15 keto-13,14 dihydro derivatives of both PGE2 and PGF2alpha. Hypertonic sucrose solutions resulted in concentration-dependent increases in prostaglandin release, particularly of PGE2 and its metabolite. It is suggested that PG's may play a role in the local effects of luminal hyperosomolarity on digestive tract functions.

Ionophores stimulate prostaglandin and thromboxane biosynthesis

The role of calcium in triggering prostaglandin and thromboxane synthesis was studied in several systems with ionophores of different ion specificities. Divalent cationophore A23187 stimulates prostaglandin and thromboxane production by washed human platelets in a concentration-dependent manner (0.3-9 muM). A23187 also induces an antimycin A-insensitive burst in oxygen utilization which is partially blocked by 5 mM aspirin or 10 muM indomethacin. Under our conditions, A23187 (up to 10 muM) does not appear to damage platelet membranes since it does not cause appreciable loss of lactate dehydrogenase or beta-glucuronidase. Mono- and divalent cationophore X537A also stimulates platelet thromboxane B(2) production and oxygen utilization, but monovalent cationophores nigericin, monensin A, A204, and valinomycin have no effect. The synthesis of prostaglandins E(2), D(2), and F(2alpha) by rat renal medulla mince is stimulated by 1 and 5 muM A23187 without changes in tissue ATP content, lactate output, or K(+) efflux. X537A, monensin A, and nigericin (all 5 muM) stimulate both prostaglandin output and K(+) efflux from renal medulla, while 5 muM valinomycin or A204 has no effect on either. None of the ionophores stimulates renomedullary prostaglandin production if calcium is omitted from the incubation medium. A23187 also stimulates prostaglandin production by human lymphoma cells, rat stomach and trachea preparations, and guinea pig polymorphonuclear leukocytes. These observations suggest a major role for Ca(2+) in stimulating prostaglandin and thromboxane biosynthesis, and also indicate that prostaglandin and/or thromboxane release may partially mediate some of the previously described effects of ionophores on cells and tissues.

Prostaglandin-mediated hypercalcemia in the VX2 carcinoma-bearing rabbit

Prostaglandin biosynthesis and metabolism were studied in the VX2 carcinoma-bearing rabbit, an animal model of prostaglandin-mediated hypercalcemia. All the identification and quantification of the prostaglandins were done by gas chromatography-mass spectrometry. The tumor incubated in vitro converted exogeneous arachidonic acid principally to PGE2. Biosynthesis from endogenous precursor lipids yields mainly PGE2 and PGF2alpha. The 100,000 x g supernatant fluid of the tumor did not contain any metabolizing enzymes. Significant hypercalcemia developed between the first and second week after tumor implantation. The levels of the major plasma metabolite of PGE2, 15-keto-13,14-dihydro-PGE2, became elevated at one week, had risen 25-fold by the end of the second week, and at the fourth week were elevated to 256 times the pre-incubation levels. The concentration of 15-keto-13,14-dihydro-PGF2alpha in plasma rose in parallell but to a lesser degree. 7alpha-hydroxy-5,11-diketotetranor-prostane-1,16-dioic acid, the major urinary metabolite of the E prostaglandins, was elevated two weeks after tumor implantation and rose until the fifth week. Indomethacin treatment lowered both serum calcium and the plasma level of 15-keto-13,14-dihydro-PGE2.

Biosynthesis of prostaglandin D2. 1. Formation of prostaglandin D2 by human platelets

Formation of prostaglandin D2 (PGD2) during the aggregation of platelets was determined, employing a specific bioassay. PGD2 was synthesized in human platelet rich plasma (PRP) in response to thrombin, collagen and epinephrine. Indomethacin pretreatment abolished the biosynthesis of PGD2. When thrombin treated PRP was incubated for different periods of time and denatured in the presence of SnCl2 to prevent the formation of PGD2 from endoperoxides during the extraction procedure, PGD2 formation was noted within the first minute of incubation and reached a peak level after 4 minutes. PGD2 from thrombin stimulated PRP was conclusively identified by gas chromatography-mass spectrometry. The formation of PGD2 during platelet aggregation could represent a mechanism of feedback inhibition of aggregation.

Coronary arterial smooth muscle contraction by a substance released from platelets: evidence that it is thromboxane A2

When human platelets are aggregated by thrombin, material is released that rapidly contracts strips of spirally cut porcine coronary artery. Prevention of the contraction by indomethacin suggested mediation by a prostaglandin. The contraction produced by aggregating platelets was unlike those produced by prostaglandins E2, F2alpha, G2, or H2, but resembled that evoked by thromboxane A2, which is formed by platelets during aggregation.

Effects of feeding ethyl-dihomo-gamma-linolenate on prostaglandin biosynthesis and platelet aggregation in the rabbit

1. The ethyl ester of dihomo-gamma-linolenic acid (20:3omega6) (1 g/kg/day) was fed to rabbits for 25 days. Plasma lipids and platelet aggregation were analyzed on day 1, 11, 16, 21 and 26. 2. All plasma lipid classes were greatly enriched with 20:3omega6. Arachidonic acid levels were elevated to a smaller extent. The different platelet phospholipid fractions analyzed were also highly enriched with 20:3omega6, whereas the arachidonic acid content in platelet phospholipids was significantly lower than in control animals. 3. The excretion of 7 alpha-hydroxy-5,11-diketotetranorprostane-1,16-dioic acid, the major urinary metabolite of prostaglandin E1 and E2 was increased 4.6 fold by the treatment. 4. Platelet aggregation in response to ADP, collagen and arachidonic acid did not differ at any time betweeen 20:3omega6 treated rabbits and controls. 5. It is concluded that prostaglandin E biosynthesis can be increased by enriching the prostaglandin precursor pool. Platelet aggregation in vitro is not altered by feeding ethyl 20:3omega6.

Increased arachidonate in lipids after administration to man: effects on prostaglandin biosynthesis

Ethyl arachidonate was administered orally to 4 healthy male volunteers in a dose of 6 gm daily for a 2 to 3 wk period after 10-day control period. The increased intake of this precursor of the dienoic prostaglandins resulted in significant increases in the relative and absolute amount of arachidonate in plasma triglycerides, phospholipids, and cholesteryl esters. Similar changes in lipid composition were noted in platelets. The excretion of 7alpha-hydroxy-5,11-diketotetranoprostane-1,16-dioic acid, the major urinary metabolite of E prostaglandins in man, was increased by an average of 47% in 3 of the 4 volunteers. Platelet reactivity was assessed by determining the threshold concentration of adenosine diphosphate (ADP) necessary to induce secondary, irreversible aggregation of platelet-rich plasma. This threshold concentration dropped significantly in all volunteers (10% to 60% of control values). It is concluded that the biosynthesis and function of prostaglandins can be augmented in man by oral administration of an esterified precursor fatty acid.